The world of polymers has progressed rapidly to transform material science from wood and metals of the 19th Century to the use of thermoset polymers of the mid-20th Century to the use of thermoplastic polymers of later 20th Century.
Thermoplastic elastomers (TPEs) combine the benefits of elastomeric properties of thermoset polymers, such as vulcanized rubber, with the processing properties of thermoplastic polymers. Therefore, TPEs are preferred because they can be made into articles using injection molding equipment.
The world of polymers also has explored “shape memory effect,” an ability of the polymer in one shape to be deformed to another shape non-permanently and then later having the ability to be restored to the original shape.
Polymers with a shape memory effect are multiphase polymers with a well engineered morphology. Such shape memory polymers can be polyethylene crosslinked by ionizing radiation for making a heat shrinking film or polyurethane block copolymers for medical applications. These types of polymers having shape memory effect have a Shore A hardness of at least about 70.
Blends of polymers, none of which themselves have shape memory effect, do not conventionally achieve a shape memory effect because of the lack of covalent bonds between different phases of the blended polymers, in order to control the network morphology.